JP6108249B2 - Positive electrode active material, method for producing the same, and lithium secondary battery including the same - Google Patents

Description

  The present invention relates to a positive electrode active material, a manufacturing method thereof, and a lithium secondary battery including the same.

  Lithium secondary batteries have been widely used as power sources for portable devices since they appeared in 1991 as small, light and large capacity batteries. Recently, with the rapid development of the electronics, communications and computer industries, video cameras, mobile phones, notebook computers, etc. have appeared and have been dazzlingly developed. As a power source for driving these portable electronic communication devices, lithium secondary Demand for batteries is increasing daily.

  Lithium secondary batteries have a problem in that the lifespan of the lithium secondary battery decreases rapidly due to repeated charging and discharging. In particular, such problems are more serious at high temperatures. This is because the electrolyte is decomposed by the moisture inside the battery or other influences, the active material is deteriorated, and the internal resistance of the battery is increased.

Thus, currently, can be cited _{LiNiO 2, LiMn 2 O 4,} LiFePO 4, Li (Ni x Co y Mn z) O 2 as the active positive electrode active material for lithium secondary batteries have been researched and developed. However, in the case of LiNiO ₂ , not only synthesis is not easy, but there is a problem in thermal stability, so commercialization is not easy, and in the case of LiMn ₂ O ₄ , it is partly commercialized as a low-priced product. The lifetime characteristics are not good due to structural deformation (Jahn-Teller distortion) due to Mn ³⁺ . In addition, LiFePO ₄ is excellent in low price and safety, and many studies have been made for a hybrid electric vehicle (HEV) at present. However, it is difficult to apply to other fields because of its low electric conductivity. is there.

Therefore, substances that has attracted the most limelight recently as an alternative positive electrode active material of LiCoO ₂ is _{Li (Ni x Co y Mn z} ) O 2. This material is less expensive than LiCoO ₂ and has the advantages that it can be used for high capacity and high voltage, but has the disadvantage that the rate capability and life characteristics at high temperature are not good. In order to overcome such disadvantages, a method of coating the surface of the positive electrode active material with a metal having good conductivity, or a substance such as Al, Mg, Ti, Zr, Sn, Ca, Ag, and Zn inside. Much research has been conducted on methods such as doping, and in the case of coating, a wet method is used. However, there is a big problem that the price is practically high in mass production. There is a growing trend to increase its properties through dry doping.

  For example, in Korean Patent No. 10-277796, the surface of the positive electrode active material is coated with a metal such as Mg, Al, Co, K, Na, or Ca, and heat-treated in an oxidizing atmosphere to coat the metal oxide. Technology is known.

  However, it is still difficult to solve problems such as a cracking phenomenon (crack) of the positive electrode active material, a capacity reduction and a power reduction of the secondary battery. Therefore, there is a demand for a positive electrode active material that can reduce the addition reaction between the electrolytic solution and the active material during charge and discharge, minimize the capacity reduction and output reduction of the secondary battery, and improve the life characteristics.

Korean Registered Patent No. 10-277796

  The first technical problem to be solved by the present invention is not only to minimize capacity reduction and output reduction, but also to improve life characteristics by significantly reducing the cracking phenomenon of the positive electrode active material. It is providing the positive electrode active material which can be made to make.

  The second technical problem to be solved by the present invention is to facilitate a positive electrode active material containing composite particles outside, inside, or outside and inside by adjusting the heat treatment temperature and the content of the composite particles (surface modifier). It is to provide a method that can be manufactured.

  The third technical problem to be solved by the present invention is to provide a positive electrode containing the positive electrode active material.

  A fourth technical problem to be solved by the present invention is to provide a lithium secondary battery including the positive electrode.

  In order to solve the above-described problems, the present invention includes lithium transition metal oxide particles and composite particles, and the composite particles include YSZ (yttria stabilized zirconia), GDC (gadolinia-doped ceria), and LSGM (lanthanum strontium gallium nitrate). , LSM (lanthanum strontium manganite), CSZ (Ca doped zirconia, CaO-stabilized zirconia), SSZ (Sc doped zirconia) and any one or more of these selected from the group consisting of Ni-YSZ And the composite particles are analyzed by X-ray diffraction (XRD) analysis. Sometimes provide a cathode active material characterized by having a single phase peak.

  The present invention also includes a step of mixing and heat-treating lithium transition metal oxide particles and composite particles, and the composite particles include YSZ (yttrium stabilized zirconia), GDC (gadolinia-doped carrier), LSGM (lanthanum strontium gallium nitrate glenite). ), LSM (lanthanum strontium manganite), CSZ (Ca doped zirconia, Calca stabilized zirconia), SSZ (Sc doped zirconia) and any one or more selected from the group consisting of Ni-YSZ. The manufacturing method of the positive electrode active material characterized by including this is provided.

  In addition, the present invention provides a positive electrode including the positive electrode active material.

  Furthermore, the present invention provides a lithium secondary battery including the positive electrode.

  The positive electrode active material according to an embodiment of the present invention includes a lithium-transition metal oxide particle and a specific composite particle having a single phase, thereby minimizing the capacity reduction and output reduction of the secondary battery. In addition, the structural characteristics of the composite particles have a shock absorbing effect during the positive electrode process, especially the pressing process, so that the cracking phenomenon of the positive electrode active material can be minimized. Can be further improved.

The following drawings and the like in the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the invention described above. It should not be construed as being limited to the matters described in the figures.
It is the figure which showed the prediction model of the movement path | route of lithium in the composite particle YSZ (yttria stabilized zirconia) optimized through the structural optimization of DFT (Discrete Fourier transformation). It is the graph which analyzed the ionic conductivity by the oxygen deficiency in the composite particle YSZ (yttria stabilized zirconia) optimized through the structure optimization of DFT (Discrete Fourier transformation). 6 is a graph showing life characteristics of lithium secondary batteries manufactured in Examples 5 to 7 and Comparative Example 6 of the present invention. 6 is a graph showing life characteristics of lithium secondary batteries manufactured in Example 5 and Comparative Example 7 of the present invention. 3 is a compression fracture strength graph obtained by measuring the particle strength of positive electrode active materials of Examples 1 and 3 and Comparative Example 1 of the present invention. 6 is a graph showing life characteristics of lithium secondary batteries manufactured in Example 8 and Comparative Example 9 of the present invention. 6 is a graph showing life characteristics of lithium secondary batteries manufactured in Comparative Examples 8 and 10. FIG. A positive electrode active material contains composite particles YSZ (yttria stabilized zirconia) and a graph showing the XRD analysis results of ZrO ₂ of the present invention. It is the graph which showed the XRD analysis result of the positive electrode active material of Example 4 of this invention.

  Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

  Terms and words used in this specification and claims should not be construed to be limited to ordinary and lexicographic meanings, so that the inventor can best explain his invention. In accordance with the principle that the concept of terms can be defined as appropriate, it must be interpreted into meanings and concepts consistent with the technical idea of the present invention.

  The positive electrode active material according to an embodiment of the present invention includes lithium transition metal oxide particles and composite particles, and the composite particles include YSZ (yttria stabilized zirconia), GDC (gadolinia-doped ceria), LSGM (lanthanum strontium gallium magnetite). , LSM (lanthanum strontium manganite), CSZ (Ca doped zirconia, CaO-stabilized zirconia), SSZ (Sc doped zirconia) and any one or more of these selected from the group consisting of Ni-YSZ And the composite particles are single at the time of X-ray diffraction (XRD) analysis measurement. It has a phase peak.

  The positive electrode active material according to an embodiment of the present invention includes a lithium-transition metal oxide particle and a specific composite particle having a single phase, thereby minimizing the capacity reduction and output reduction of the secondary battery. In addition, the structural characteristics of the composite particles have a shock absorption effect during the positive electrode process, especially the pressing process, so that the cracking phenomenon of the positive electrode active material can be minimized. Can be further improved.

In the positive electrode active material according to an embodiment of the present invention, YSZ of the composite particles is yttria stabilized zirconia, and is stabilized at room temperature by adding yttrium oxide (yttria) to zirconium oxide (zirconia). This is a ceramic material. As for YSZ, by adding yttria to zirconia, a part of Zr ⁴⁺ ions can be ^replaced with Y ³⁺ . Thereby, instead of 4 O ²⁻ ions, 3 O ²⁻ ions can be substituted, resulting in an oxygen deficiency. Due to the oxygen deficiency generated in this way, YSZ has O ²⁻ ion conductivity, and the higher the temperature, the better the conductivity. Such features can be usefully used in solid oxide fuel cells (SOFC) operating at high temperatures.

  Also, in the cathode active material according to an embodiment of the present invention, LSGM of the composite particles has high ionic conductivity as lanthanum-strontium-gallium-magnesium oxide (LaSrGaMg), so that the operating temperature of the solid oxide fuel cell is reduced. A substance that can be lowered.

Further, in the positive electrode active material according to an embodiment of the present invention, among the composite particles, GDC is ceria doped with gadolinium (Gd), for example, Gd _0.1 Ce _0.9 O _1.95. And has high ionic conductivity similar to LSGM.

In the positive electrode active material according to an embodiment of the present invention, LSM in the composite particles has a manganese-based perovskite structure, for example, LaSrMnO or La _(1-x) Sr _x MnO ₃ (0.01 ≦ x ≦ 0.30) Perovskite structure, almost no ionic conductivity, and excellent electron conductivity. La _1-x Sr _x Mn _y O _3-δ (0.05 ≦ x ≦ 1) (0.95 ≦ y ≦ 1.15) (δ is a numerical value indicating a small deviation from the perfect stoichiometry) As defined).

In the positive electrode active material according to the embodiment of the present invention, among the composite particles, SSZ is (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _X , (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _{x- z} (Y ₂ O ₃ ) _z or (ZrO ₂ ) _1-2x-z (Sc ₂ O ₃ ) _x (CeO ₂ ) _z (0 <x ≦ 0.25) (0 <z ≦ 0.1) obtain.

  Also, in the positive electrode active material according to an embodiment of the present invention, among the composite particles, CSZ may be calcium-doped zirconia or calcia-stabilized zirconia, and heat of zirconia by adding calcia. Stability can be improved. CSZ is a state in which a cubic crystal structure and a tetragonal crystal structure are mixed. The tetragonal crystal structure changes to a cubic crystal structure when the temperature rises, and again changes to the tetragonal crystal structure when the temperature decreases, and volume expansion and contraction can be repeated in the process of changing the crystal structure.

  In the cathode active material according to an embodiment of the present invention, the composite particles YSZ, GDC, LSGM, LSM, CSZ, SSZ and Ni-YSZ have a single phase.

  In the positive electrode active material according to an embodiment of the present invention, the composite particles are preferably any one selected from the group consisting of YSZ, CSZ and SSZ, or a mixture of two or more thereof, which is zirconia-based.

In particular, YSZ is _{Zr (1-x) Y x} O 2-x / 2, be a 0.01 ≦ x ≦ 0.30, preferably may be 0.03 ≦ x ≦ 0.20.

SSZ is preferably (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _X , (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _xz (Y ₂ O ₃ ) _z or (ZrO ₂ ) _{1 −2x−z} (Sc ₂ O ₃ ) _x (CeO ₂ ) _z (0.01 ≦ x ≦ 0.2) (0.01 ≦ z ≦ 0.1).

  The CSZ preferably has a CaO content of 2% to 17% by weight based on the total weight of the CSZ.

  The cathode active material according to the first embodiment of the present invention includes lithium transition metal oxide particles and composite particles, and the composite particles may be coated on the outer surface of the lithium transition metal oxide particles to form a coating layer.

  Specifically, for example, when the composite particle is YSZ and YSZ is included in the outer surface of the lithium transition metal oxide, Y can enter the Zr site to form a single phase first, When the positive electrode active material structure has a superstructure, oxygen deficiency occurs in the structure, and a lot of space is generated on the surface of the positive electrode active material.

  FIGS. 1 and 2 illustrate composite particles YSZ (yttriz stabile) obtained by optimizing YSZ (yttria stabilized zirconia) included in a positive electrode active material according to an embodiment of the present invention through structural optimization of DFT (Discrete Fourier transformation). FIG. 7 is a diagram in which prediction modeling of a lithium movement path in zirconia) and ionic conductivity of lithium ions are comparatively analyzed.

  As shown in FIG. 1, if the lithium transfer path is examined with the optimized YSZ, Li can pass through the surface of the positive electrode active material due to the empty space due to oxygen deficiency inside the YSZ structure. It can be seen that a lot of space is created.

  Further, as shown in FIG. 2, as a result of searching for a path through which lithium ions can pass through YSZ through DFT and analyzing the ionic conductivity of lithium ions, the path (Path) 2-3-4 in FIG. It can be confirmed that an energy difference of about 1.0 eV is shown in the section.

  If a path with oxygen deficiency is connected through this, the lithium ion conductivity can be very high, and the cathode active material containing composite particles YSZ is applied to the secondary battery due to such oxygen deficiency. Capacitance reduction or output reduction can be minimized.

  Therefore, according to one embodiment of the present invention, YSZ is oxygen deficient in proportion to the amount of Y element, and according to one embodiment of the present invention, YSZ is an outer surface of lithium transition metal oxide particles. When coated, the oxygen deficiency may range from 0.25 ppm to 4500 ppm relative to the total positive electrode active material.

  In addition, the formation of the structurally vacant space has an impact absorbing effect during the positive electrode process, particularly during the press process, so that the cracking phenomenon of the positive electrode active material can be minimized.

  For example, the positive electrode active material according to an embodiment of the present invention may have a compressive strength of 80 to 500 MPa, preferably 100 to 200 MPa under a pressure of 0.5 to 10 mN.

  The pressure is measured by applying pressure to the positive electrode active material with a force of 0.5 to 10 mN using, for example, a micro compression tester, and measuring the time point at which cracking of the particles is generated. ).

  In the cathode active material according to the first embodiment of the present invention, the composite particles may be coated in a thickness range of 1 to 5000 nm from the outer surface of the lithium transition metal oxide particles.

  The positive active material according to the second embodiment of the present invention may include lithium transition metal oxide particles and composite particles, and the composite particles may be included in the lithium transition metal oxide particles.

  The positive electrode active material according to an embodiment of the present invention includes a composite particle included in a lithium transition metal oxide particle, and a structural crystal collapse of the positive electrode active material by forming a composite with the lithium transition metal oxide particle. And structural stability and electrochemical properties can be improved.

  Specifically, according to one embodiment of the present invention, the composite particles have a concentration gradient that decreases from the surface of the lithium transition metal oxide particles toward the inside, along with the lithium transition metal oxide particles. It can be combined to form a complex.

  For example, in the cathode active material of the present invention, the composite particles may have a lithium transition metal oxide particle content in the external bulk that is at least 20% higher than the content in the internal bulk, The center of the metal oxide particle and its peripheral region may mean a region containing 50% of the number of transition metal atoms of the entire particle.

  When YSZ is coated inside lithium transition metal oxide particles according to an embodiment of the present invention, the oxygen deficiency may specifically range from 0.25 to 4500 ppm.

  The composite particles may be included in a thickness range of 1 to 5000 nm in the internal direction of the lithium transition metal oxide particles.

  The positive active material according to the third embodiment of the present invention includes lithium transition metal oxide particles and composite particles, and the composite particles are coated on the outer surface of the lithium transition metal oxide particles to form a coating layer. The transition metal oxide particles can be included together with the lithium transition metal oxide particles.

  The composite particles have a concentration gradient that decreases from the surface to the inside of the lithium transition metal oxide particles, and can be combined with the lithium transition metal oxide particles to form a composite.

  In addition, when YSZ is included both inside and outside the lithium transition metal oxide particles according to an embodiment of the present invention, it may be in the range of 50 to 30000 ppm with respect to the whole positive electrode active material.

  According to an embodiment of the present invention, the composite particles may be included in an amount of 50 ppm to 30000 ppm, specifically 100 ppm to 20000 ppm, based on the total positive electrode active material.

  The average particle diameter of the positive electrode active material is preferably 3 μm to 30 μm.

  The cathode active material according to an embodiment of the present invention may further include an oxide including one or more elements of Ca, Nb, W, Mg, Ti, B, Mo, and Zr in the coating layer.

  The oxide containing one or more elements of Ca, Nb, W, Mg, Ti, B, Mo, and Zr may be included in the coating layer in an amount of 50 ppm to 30000 ppm.

In the cathode active material according to an embodiment of the present invention, the lithium transition metal oxide particles may include a compound represented by the following chemical formula (1):
Li _{(1 + a)} Ni _(1-bc) Mn _(b) Co _(c) M ′ _(s) M ″ _(v) O ₂ (1)
In the chemical formula (1), M ′ represents any one selected from the group consisting of Y, Zr, La, Sr, Ga, Mg, Mn, Ca, Sc and Ni, or a mixed element of two or more of these. Including
M ″ is one or more elements of Ca, Nb, W, Mg, Ti, B, Mo, Sc and Zr;
0 ≦ a <0.2, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ s ≦ 0.2, and 0 ≦ v ≦ 0.2.

  According to one embodiment of the present invention, in chemical formula (1), 0 ≦ a <0.2, and M ′ is any one selected from the group consisting of Zr, Y, Ca, Sc and Ni, or Among these, it is preferable to include two or more mixed elements, and s and v may have a concentration gradient that decreases from the surface of the lithium transition metal oxide particle toward the inside.

  In addition, according to an embodiment of the present invention, in the chemical formula (1), specifically, 0 ≦ a ≦ 0.09, and more specifically, a = 0.

In the chemical formula (1), when a is more than 0.09, especially when a is 0.2 or more, the effect of coating the lithium transition metal particles with composite particles (for example, YSZ) is to coat other oxides (for example, ZrO ₂ ). The difference in the life characteristic effect may not be remarkably within about 10% as compared with the case of the above. On the other hand, in the chemical formula (1), when a is 0.09 or less, especially when a is 0, the effect of coating the composite particles on the lithium transition metal particles is longer than that of the case of coating with other oxides. May represent a significant difference from 30% to 70%.

  Meanwhile, the present invention provides a method for producing a positive electrode active material.

A method of manufacturing a positive electrode active material according to an embodiment of the present invention includes a step of mixing and heat treating lithium transition metal oxide particles and composite particles, and the composite particles include YSZ (yttrium stabilized zirconia) and GDC (gadolinia-doped carrier). ), LSGM (LaSrGaMg), LSM (La _(1-x) Sr _x MnO ₃ ), CSZ, SSZ and Ni—YSZ, or a mixture of two or more thereof be able to.

  According to an embodiment of the present invention, the composite particles preferably include any one selected from the group consisting of YSZ, CSZ, and SSZ, or a mixture of two or more thereof.

  According to one embodiment of the present invention, the heat treatment may be performed at a temperature range of 100 ° C. to 1200 ° C. for 4 hours to 24 hours.

  According to a method for manufacturing a positive electrode active material according to an embodiment of the present invention, a lithium transition metal oxide including a coating layer formed on the surface of a lithium transition metal oxide particle or a composite particle inside the lithium transition metal oxide particle. Forming the composite with the particles can affect the heat treatment temperature and time during the heat treatment after mixing the positive electrode active material and the composite particles.

  According to an embodiment of the present invention, for example, when the heat treatment is performed in a temperature range of 100 ° C. to 600 ° C., the coating layer can be formed on the outer surface of the lithium transition metal oxide particles by the heat treatment.

  That is, when heat treatment is performed in a temperature range of 100 ° C. to 600 ° C., a coating layer is formed on the surface of the lithium transition metal oxide particles, and the coating layer is made of YSZ, GDC, LSGM, LSM, CSZ, SSZ, and Ni—YSZ. A positive electrode active material containing any one selected from the group or a mixture of two or more thereof and containing composite particles having a single-phase peak at the time of XRD measurement can be obtained.

  According to an embodiment of the present invention, a part of the composite particles may be included in the lithium transition metal oxide even in the heat treatment in the temperature range of 100 ° C. to 600 ° C. In this case, the composite particles It has a concentration gradient that decreases from the surface to the inside of the lithium transition metal oxide particles, and is contained in the surface of the lithium transition metal oxide particles and inside the lithium transition metal oxide particles, and is combined with the lithium transition metal oxide particles. To form a complex. In this case, the composite particles can be present from the surface to the inside of the lithium transition metal oxide particles, for example, up to about 500 nm.

  Further, according to an embodiment of the present invention, for example, when heat treatment is performed in a temperature range of 600 ° C. to 1200 ° C., a positive electrode active material including composite particles inside lithium transition metal oxide particles can be obtained by heat treatment, At this time, as described above, the composite particles may include any one selected from the group consisting of YSZ, GDC, LSGM, LSM, CSZ, SSZ, and Ni-YSZ, or a mixture of two or more thereof. .

  At this time, the composite particles have a concentration gradient that decreases from the surface to the inside of the lithium transition metal oxide particles, and can be combined with the lithium transition metal oxide particles to form a composite. In this case, the composite particles can exist from the surface to the inside of the lithium transition metal oxide particles, for example, up to about 500 nm or more.

  According to an embodiment of the present invention, composite particles can exist on the outer surface of the lithium transition metal oxide even when heat treatment is performed in a temperature range of 600 ° C. to 1200 ° C.

According to the method for producing a positive electrode active material according to an embodiment of the present invention, the transition metal oxide particles include lithium transition metal composite oxide particles represented by the following chemical formula (1), and s and v below are lithium transition metal oxide particles. Can have a concentration gradient that decreases from the surface to the interior:
Li _{(1 + a)} Ni _(1-bc) Mn _(b) Co _(c) M ′ _(s) M ″ _(v) O ₂ (1)
In the chemical formula (1), M ′, M ″, a, b, c, s, and v are as described above.

According to the method for producing a positive electrode active material according to an embodiment of the present invention, the composite particles used as the surface modifier have an average particle size (D ₅₀ ) of 5 nm to 500 nm, preferably 20 nm to 200 nm, more preferably 30 nm. To 100 nm is preferred.

In the present invention, the average particle size (D ₅₀ ) of the composite particles can be defined as the particle size based on 50% of the particle size distribution. The average particle size (D ₅₀ ) of the particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle diameter of about several millimeters from a submicron region, and can obtain high reproducibility and high resolution results.

For example, the YSZ average particle diameter (D ₅₀ ) is measured by dispersing YSZ in a solution and then introducing it into a commercially available laser diffraction particle size measuring device (for example, Microtrac MT3000) to output an ultrasonic wave of about 28 kHz. After irradiation at 60 W, the average particle size (D ₅₀ ) based on 50% of the particle size distribution in the measuring device can be calculated.

  According to one embodiment of the present invention, the surface modifier (composite particles) can be used in an amount of 50 ppm to 30000 ppm.

  According to the method for manufacturing a positive electrode active material according to an embodiment of the present invention, a dry mixing method or a wet mixing method can be used for mixing.

  In the manufacturing method according to an embodiment of the present invention, the dry mixing method can be performed using a mixing method using a shaker, a mortar grinder mixing method, and a mixing method using a mechanical milling method, preferably a mechanical method. It is preferable to use a mechanical milling method in forming a uniform coating layer.

  If it examines concretely, the mixing method by a shaker may be performed by hand-mixing lithium transition metal oxide particles and composite particles and mixing them by shaking several times.

  The mortar grinder mixing method is a method in which lithium transition metal oxide particles and composite particles are uniformly mixed using mortar.

  The mechanical milling method includes, for example, a roll mill, a ball mill, a high energy ball mill, a planetary mill, a stirred ball mill, and a vibration mill. (Vibrating mill) or jet mill (jet mill), lithium transition metal oxide particles and composite particles can be mixed by mechanical friction, for example, by rotating at a rotational speed of 100 rpm to 1000 rpm. Compressive stress can be applied.

  Moreover, this invention provides the positive electrode containing a positive electrode active material.

  The positive electrode can be produced by a conventional method known in the art. For example, a slurry is prepared by mixing and stirring a positive electrode active material with a solvent, and if necessary, a binder, a conductive agent, and a dispersing agent. Then, the slurry is applied (coating) to a current collector of metal material, compressed, and then dried. Thus, the positive electrode can be manufactured.

  The current collector of the metal material is a highly conductive metal, and any metal can be used as long as the positive electrode active material slurry can be easily bonded to the battery in the voltage range of the battery. Non-limiting examples of positive electrode current collectors include foils made from aluminum, nickel, or combinations thereof.

  Solvents for forming the positive electrode include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide, or water. These solvents may be used alone or in combination of two or more. Can be used. The amount of the solvent used is sufficient as long as it can dissolve and disperse the positive electrode active material, the binder, and the conductive agent in consideration of the coating thickness of the slurry and the production yield.

  As the binder, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, cellulose alcohol, polyvinyl MC, methyl alcohol , Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly Acrylic acid (poly ac various types of binder polymers such as lylic acid) and polymers obtained by substituting these hydrogens with Li, Na, or Ca, or various copolymers.

  The conductive agent is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, acetylene black, ketjen Carbon black such as black, channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; conductive tube such as carbon nanotube; metal powder such as fluorocarbon, aluminum and nickel powder; zinc oxide Conductive whiskers such as potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

  As the dispersant, an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone can be used.

  The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

  As the negative electrode active material used in the negative electrode according to an embodiment of the present invention, a carbon material, lithium metal, silicon, tin, or the like that can occlude and release lithium ions can be generally used. Preferably, a carbon material can be used, but as the carbon material, both low crystal carbon and high crystal carbon can be used. Typical examples of the low crystalline carbon include soft carbon and hard carbon, and examples of the high crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, and liquid crystal. Pitch-based carbon fibers (mesophase pitch based carbon fibers), carbon microspheres (meso-carbon microbeads), liquid crystal pitches (Mesophase pitches), and petroleum and coal-based coke (high temperature) Is.

  Further, the negative electrode current collector is generally produced to a thickness of 3 μm to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired A surface of carbon, copper or stainless steel that has been surface-treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. Also, like the positive electrode current collector, it is possible to reinforce the binding force of the negative electrode active material by forming fine irregularities on the surface, such as films, sheets, foils, nets, porous bodies, foams, nonwoven fabric bodies, etc. It can be used in various forms.

  As the binder and the conductive agent used for the negative electrode, those that can be usually used in this field can be used in the same manner as the positive electrode. The negative electrode can be produced by mixing and stirring a negative electrode active material, an additive, and the like to produce a negative electrode active material slurry, and then applying the slurry to a current collector and compressing the slurry.

  The separator may be a conventional porous polymer film conventionally used as a separator, such as an ethylene homopolymer, a propylene homopolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-methacrylate copolymer. A porous polymer film made of a polyolefin polymer such as a polymer can be used alone or by laminating these, or an ordinary porous nonwoven fabric such as high-melting glass fiber, polyethylene terephthalate fiber, etc. Although the nonwoven fabric which consists of can be used, it is not limited to this.

The lithium salt that can be included as the electrolyte used in the present invention can be used without limitation as those commonly used in electrolytes for lithium secondary batteries. For example, the anion of the lithium salt includes F ⁻ , Cl ⁻ , Br ⁻ , and the like. I ⁻ , NO ₃ ⁻ , N (CN) ₂ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , (CF ₃ ) ₂ PF ₄ ⁻ , (CF ₃ ) ₃ PF ₃ ⁻ , (CF ₃ ) ₄ PF _{^{2 -, (CF 3) 5}} PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N - , CF ₃ CF ₂ (CF ₃ ) ₂ CO ⁻ , (CF ₃ SO ₂ ) ₂ CH ⁻ , (SF ₅ ) ₃ C ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , CF ₃ (CF ₂ ) ₇ SO ₃ ⁻ , CF ₃ CO ₂ ⁻ , CH ₃ C It may be any one selected from the group consisting of O ₂ ⁻ , SCN ⁻ and (CF ₃ CF ₂ SO ₂ ) ₂ N ^— .

  Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used when manufacturing a lithium secondary battery. However, the present invention is not limited to these examples.

  The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

  The lithium secondary battery according to the present invention can be preferably used not only as a battery cell used as a power source of a small device but also as a unit battery in a medium-sized battery module including a large number of battery cells.

  Preferable examples of the medium-sized device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

(Example)
Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into several different forms, and the scope of the present invention should not be construed as being limited to the embodiments detailed below. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

  Hereinafter, although an example and an experiment example are given and explained further, the present invention is not restricted by these examples and experiment examples.

<Production of lithium transition metal oxide>
(Production Example 1)
A speed at which the center rpm of the experimental mixer is 18000, with 55.84 g of LiOH (H ₂ O) and 123.61 g of Ni _0.6 Mn _0.2 Co _0.2 (OH) ₂ having an average particle diameter of 12 μm. And mixed for 1 minute.

The precursor thus obtained was placed in a 500 cc alumina crucible and fired at about 900 ° C. for 6 hours in an air atmosphere. The cake obtained after baking was crushed and then dispensed using a 400 mesh sieve [Tyler Standard Screen Scale, USA] to obtain LiNi _0.6 Mn _0.2 Co _{0. 2} O ₂ was obtained.

<Manufacture of positive electrode active material>
Example 1
LiNi _0.6 Mn _0.2 Co _0.2 O ₂ 118.4 g and 50 nm YSZ (Zr _0.84 Y _0.16 O _1.92 ) 1.6 g were mixed in a dry mixer (Laedige Mixer, Inc.) (Matsubo Manufacture, FM-130D type), mixed for 1 minute, heat-treated at 900 ° C. for 6 hours in a baking furnace, pulverized in a mortar and sieved, and LiNi _0.6 Mn _0. A positive electrode active material containing YSZ inside ₂ Co _0.2 O ₂ was obtained.

(Example 2)
In Example _1, except for the _{YSZ (Zr 0.84 Y 0.16 O 1.92} ) YSZ (Zr 0.84 Y 0.16 O 1.92) instead of 1.6g to put 3.16g In the same manner as in Example 1, a positive electrode active material was obtained.

(Example 3)
A positive electrode in which the outer surface of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ was coated with YSZ except that the heat treatment was performed at 500 ° C. for 6 hours. An active material was obtained.

Example 4
In Example 1, except that LiNi _0.8 Mn _0.1 Co _0.1 O ₂ was used instead of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ and the heat treatment was performed at 550 ° C. In the same manner as in Example 1, a positive electrode active material containing YSZ on the outer surface and inside of LiNi _0.8 Mn _0.1 Co _0.1 O ₂ was obtained.

(Comparative Example 1)
Production Example 1 was used as a positive electrode active material.

(Comparative Example 2)
Li _1.2 Ni _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1.2) instead of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (Li / M = 1) ) Was used in the same manner as in Example 1 to obtain a positive electrode active material.

(Comparative Example 3)
Li _1.2 Ni _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1.2) instead of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (Li / M = 1) The positive electrode active material was obtained in the same manner as in Example 4 except that 1.6 g of ZrO ₂ was used instead of YSZ.

(Comparative Example 4)
Using LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1) instead of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (Li / M = 1), YSZ A positive electrode active material was obtained in the same manner as in Example 4 except that 3.16 g of ZrO ₂ was used instead of and heat treatment was performed at 550 ° C.

(Comparative Example 5)
Li _1.2 Ni _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1.2) instead of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (Li / M = 1) ) Was used in the same manner as in Example 4 to obtain a positive electrode active material.

<Manufacture of lithium secondary batteries>
(Example 5)
(Manufacture of positive electrode)
94% by weight of the positive electrode active material prepared in Example 1, 3% by weight of carbon black as a conductive agent, 3% by weight of polyvinylidene fluoride (PVdF) as a binder, N-methyl-2-2 as a solvent A positive electrode mixture slurry was prepared by adding to pyrrolidone (NMP). The positive electrode mixture slurry was applied to an aluminum (Al) thin film, which is a positive electrode current collector having a thickness of about 20 μm, and dried to produce a positive electrode, and then a roll press was performed to produce a positive electrode.

(Manufacture of negative electrode)
Carbon powder 96.3% by weight as the negative electrode active material, super-p 1.0% by weight as the conductive agent, and styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as the binder 1.5% by weight and 1.2% by weight. %, And added to NMP as a solvent to produce a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper (Cu) thin film, which was a negative electrode current collector having a thickness of 10 μm, and dried to produce a negative electrode, and then a roll press was performed to produce a negative electrode.

(Manufacture of non-aqueous electrolyte)
On the other hand, LiPF ₆ was added to a non-aqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 30:70 as an electrolyte to produce a 1M LiPF ₆ non-aqueous electrolyte.

(Manufacture of lithium secondary batteries)
After the positive electrode and the negative electrode manufactured in this way are mixed with a polyethylene / polypropylene mixed separator, a polymer type battery is manufactured by an ordinary method, and then the manufactured non-aqueous electrolyte is injected to recharge the lithium secondary battery. Completed battery manufacturing.

(Examples 6 to 8)
A lithium secondary battery was manufactured in the same manner as in Example 5 except that each of the positive electrode active materials manufactured in Examples 2 to 4 was used.

(Comparative Examples 6 to 10)
A lithium secondary battery was manufactured in the same manner as in Example 5 except that each of the positive electrode active materials manufactured in Comparative Examples 1 to 5 was used.

  The composition of the examples and comparative examples can be summarized as follows:

(Experimental example 1: Electrochemical experiment 1)
<Cycle characteristic evaluation experiment>
In order to examine the relative efficiency according to the number of cycles for the lithium secondary batteries obtained in Examples 5 to 7 and Comparative Examples 6 and 7, an electrochemical evaluation experiment was performed as follows.

  Specifically, the lithium secondary batteries obtained in Examples 5 to 7 and Comparative Examples 6 and 7 were charged from 45 ° C. until a constant current (CC) of 1C reached 4.35 V, and then a constant voltage of 4.35 V ( CV) and the first charge was performed until the charge current reached 0.05 mAh. Then, after leaving it for 20 minutes, it discharged until it became 3.0V with the constant current of 2C (cut-off was performed at 0.05C). This was repeated for 1 to 29 cycles and 1 to 49 cycles. The results are shown in FIGS. 3 and 4, respectively.

  If it examines concretely, FIG. 3 is the figure which showed the lifetime characteristic graph of the lithium secondary battery of Examples 5-7 and the comparative example 6. FIG.

  As can be seen from FIG. 3, in the case of the lithium secondary batteries of Examples 5 to 7, it can be confirmed that the gradient with respect to the relative efficiency from 1 to 29 cycles is gentler than that of Comparative Example 6. It was also found that in Examples, as in Examples 5 and 6, the life characteristics were also affected by the amount of YSZ used during the production of the positive electrode active material.

  That is, when the amount of YSZ used is increased approximately twice, it can be confirmed that the relative capacity (%) decreases as the number of cycles increases. Specifically, Example 5 and Example 6 showed similar relative capacities up to 10 cycles, but it was confirmed that Example 6 slightly decreased compared to Example 5 after 10 times.

  On the other hand, in the case of Examples 5 and 6, it can be seen that the life characteristics are improved by about 3% or more as compared with Comparative Example 6.

On the other hand, in the case of the lithium secondary battery of Example 7 using the positive electrode active material in which the heat treatment temperature was lowered and YSZ was coated on the outer surface of LiNi _0.6 Mn _0.2 Co _0.2 , the lifetime characteristics were most excellent. I understand that.

  On the other hand, in the case of the comparative example 6 which does not contain YSZ inside or outside, it was confirmed that the slope suddenly dropped from 3 cycles and decreased by 4% or more in 29 cycles.

  Therefore, it can be seen that the inclusion of lithium transition metal oxide particles and composite particles according to the embodiment of the present invention can relieve cycle deterioration of the secondary battery and exhibit stable cycle characteristics for a long period of time.

  On the other hand, FIG. 4 is a graph showing the results of graphs of the life characteristics of Example 5 and Comparative Example 7 containing YSZ in order to compare the life characteristics depending on the amount of lithium of the lithium transition metal oxide particles. Charging / discharging was performed in the same manner as in FIG. 3, but repeated between 1 and 49 cycles.

  Considering FIG. 4, the lithium secondary battery of Example 5 using YSZ as the positive electrode active material and using the positive electrode active material whose Li / transition metal (M) is 1 contains YSZ, and Li / transition. It can be seen that the life characteristics are remarkably excellent as compared with the lithium secondary battery of Comparative Example 7 using a positive electrode active material having a metal (M) of 1.2 and an excessive amount of lithium.

  That is, the slopes of Example 5 and Comparative Example 7 were similar up to about the 10th cycle, but after the 10th cycle, it was found that the life characteristics of the lithium secondary battery of Comparative Example 7 were significantly reduced. It can be seen that the lithium secondary battery of Example 5 is increased by about 10% or more as compared with the lithium secondary battery of Comparative Example 7.

(Experimental example 2: Experiment of compressive fracture strength)
In order to measure the intensity | strength of the particle | grains of the positive electrode active material of Example 1 and 3 and the comparative example 1, it evaluated with the micro compression tester (Micro compression tester), The result was shown in FIG.

  In the pressure measurement, the positive electrode active material samples of Examples 1 and 3 and Comparative Example 1 were used to apply pressure with a force of 0.5 to 10 mN and measure the time point when cracks were generated in the particles. MPa).

  Considering FIG. 5, in the case of Examples 1 and 3 containing YSZ inside and outside the lithium transition metal oxide particles, it is about 1.5 as compared with Comparative Example 1 which is a positive electrode active material not containing YSZ. It can be seen that the compressive fracture strength (MPa) increases by about 2 to 2 times.

  Specifically, in the case of Example 3 including YSZ outside the lithium transition metal oxide particles, the compressive fracture strength (MPa) is 120 MPa, and the lithium transition metal oxide particles include YSZ. In the case of Example 1, the compressive fracture strength (MPa) was 118 MPa.

  On the other hand, in the case of lithium transition metal oxide particles not containing YSZ as in Comparative Example 1, the compressive fracture strength (MPa) decreased by about 50% in Examples 1 and 3 was only 60 MPa.

  It can be predicted that the positive electrode active material of the present invention includes YSZ, and thus has a further excellent impact absorption effect due to the presence of oxygen deficiency (oxygen vacancy).

  From FIG. 5, it can be seen that the inclusion of YSZ has an impact absorbing effect during the pressing process, so that the cracking phenomenon of the positive electrode active material can be minimized.

(Experimental example 3: Electrochemical experiment 2)
<Experiment on cycle characteristics evaluation based on lithium content and coating layer components>
In order to examine the relative efficiency of the lithium secondary batteries obtained in Example 8 and Comparative Examples 8 to 10 depending on the amount of lithium and the components of the coating layer, an electrochemical evaluation experiment was performed as follows.

  Specifically, the lithium secondary batteries obtained in Example 8 and Comparative Examples 8 to 10 were charged at 45 ° C. until a constant current (CC) of 1 C reached 4.2 V, and then a constant voltage (CV) of 4.2 V. The first charge was performed until the charge current reached 0.05 mAh. Then, after leaving it for 20 minutes, it discharged until it became 3.0V with the constant current of 1C (cut-off was performed at 0.05C). This was repeated for 1 to 200 cycles. The results are shown in FIGS.

Come to specifically study, 6 _is an diagram comparing the life characteristics of the rechargeable battery when it is _{LiNi 0.8 Mn 0.1 Co 0.1 O 2} (Li / M = 1) FIG. 7 compares the life characteristics (relative capacity%) of the secondary battery in the case of Li _1.2 Ni _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1.2). FIG.

As shown in FIG. 6, in the case of LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1), secondary using a positive electrode active material containing YSZ inside and outside the positive electrode active material. Comparing the life characteristics of the battery (Example 8) with the life characteristics of the secondary battery (Comparative Example 9) using the positive electrode active material containing ZrO ₂ , it is 50% or more from the first cycle to the 200th cycle. A significant difference in relative capacity (%) was shown.

On the other hand, in the case of Li _1.2 Ni _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1.2) as shown in FIG. The life characteristics of the secondary battery using the positive electrode active material (Comparative Example 10) contained in the battery are compared with the life characteristics of the secondary battery using the positive electrode active material containing ZrO ₂ (Comparative Example 8). From the first to the 200th cycle, similar relative capacity (%) values were shown.

From the above results, when composite particles such as YSZ are used according to the examples of the present invention, the lithium transition metal oxide particles Li / M = 1, compared to the lithium excess Li / M = 1.2. It can be seen that the life characteristics are further affected by representing a significant difference compared to the secondary battery containing ZrO ₂ .

(Experimental example 4: Measurement of X-ray diffraction (XRD) analysis)
In order to comparatively analyze the XRD phases of YSZ and ZrO ₂ contained in the positive electrode active material of the present invention, XRD diffraction measurement using Cu (Kα-line) was performed on YSZ and ZrO ₂ , and the result Is shown in FIG.
-Target: Cu (Kα-ray) graphite monochromator-Slit: Diverging slit = 0.5 degree, receiving slit = 9.55 mm, scattering slit = 5.89 degree-Measurement area and step angle / measurement time :
−10.0 degrees <2θ <90 degrees, 0.5 seconds, 0.024 degrees, where 2θ represents a diffraction angle.

When FIG. 8 is examined, it can be confirmed that YSZ has a cubic crystal structure, but a monoclinic crystal structure of ZrO ₂ (Monoclinic Crystal structure), and YSZ has a main peak. It can be seen that 2θ of (main peak) has a single-phase peak present at 29 to 31 degrees, and it can be confirmed that the YSZ peak is clearly separated from the ZrO ₂ peak not present in the single phase. In particular, the main peak of ZrO ₂ exists between 27.5 and 28.5 degrees, and the secondary peak also exists between 31.1 and 31.8 degrees. Since the position of the main peak is remarkably different, YSZ and ZrO ₂ are fundamentally different phases, and it can be considered that the characteristics of crystallinity are completely different.

FIG. 9 is a graph showing a result of analyzing LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1) containing YSZ of Example 4 under the same XRD measurement conditions.

As can be seen in FIG. 9, the 2θ of the YSZ peak observed in FIG. 8 is 27.5 to 28 in LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (Li / M = 1) of Example 4. It can be confirmed that it appears at 5 degrees.

  That is, the YSZ composite phase is present on the outer surface of the positive electrode active material, and is present on the inner surface side in the form of a composite. In the case of YSZ contained in the positive electrode active material, the secondary phase does not appear, and it appears as a single phase that the layered system has. That is, it can be seen as a result that single-phase YSZ is present inside and outside the positive electrode active material in a composite form.

Claims (36)

Lithium transition metal oxide particles; and composite particles,
The composite particles include any one selected from the group consisting of YSZ, GDC, LSGM, LSM, CSZ, SSZ and Ni-YSZ, or a mixture of two or more thereof.
Wherein the composite particles have a single phase peak at X-ray diffraction (XRD) analysis measurement,
The positive electrode active material, wherein the lithium transition metal oxide particles include a compound represented by the following chemical formula (1) :
Li _{(1 + a)} Ni _(1-bc) Mn _(b) Co _(c) M ′ _(s) M ″ _(v) O ₂ (1)
In the chemical formula (1), M ′ is any one selected from the group consisting of Y, Zr, La, Sr, Ga, Mg, Mn, Ca, Sc and Ni, or a mixed element of two or more of these. Including
M ″ is one or more elements of Ca, Nb, W, Mg, Ti, B, Mo, Sc and Zr;
0 ≦ a <0.2, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ s ≦ 0.2, and 0 ≦ v ≦ 0.2 .   The cathode active material according to claim 1, wherein the composite particles are coated on an outer surface of the lithium transition metal oxide particles to form a coating layer.   The cathode active material according to claim 1, wherein the composite particles are contained in the lithium transition metal oxide particles.   The composite particles have a concentration gradient that decreases toward the inside from the surface of the lithium transition metal oxide particles, and are combined with the lithium transition metal oxide particles to form a composite, The positive electrode active material according to claim 3. The composite particles have a content in the outer bulk of the lithium transition metal oxide particles that is at least 20% higher than the content in the inner bulk;
The internal bulk is a region including the center and the peripheral region of the lithium transition metal oxide particle and including 50% of the number of transition metal atoms of the entire particle. Positive electrode active material.   5. The positive electrode active material according to claim 4, wherein the composite particles are included in a thickness range of 1 to 5000 nm in the internal direction from the surface of the lithium transition metal oxide particles.   The cathode active material according to claim 2, wherein the composite particles are coated in a thickness range of 1 to 5000 nm from an outer surface of the lithium transition metal oxide particles.   The composite particles are coated on the outer surface of the lithium transition metal oxide particles to form a coating layer, and are included together with the lithium transition metal oxide particles inside the lithium transition metal oxide particles. The positive electrode active material according to claim 1.   The positive electrode active material according to claim 8, wherein the composite particles are included in an amount of 50 ppm to 30000 ppm with respect to the whole positive electrode active material.   The composite particles have a concentration gradient that decreases toward the inside from the surface of the lithium transition metal oxide particles, and are combined with the lithium transition metal oxide particles to form a composite, The positive electrode active material according to claim 8.   2. The positive electrode active material according to claim 1, wherein the composite particles include any one selected from the group consisting of YSZ, CSZ, and SSZ, or two or more thereof.   The cathode active material according to claim 11, wherein the YSZ is oxygen deficient in proportion to the amount of element Y. The positive electrode active material according to claim 12, wherein the YSZ is Zr _(1-x) Y _x O _{2-x / 2} (0.01 ≦ x ≦ 0.30).   The cathode active material according to claim 12, wherein the amount of oxygen deficiency is in the range of 0.25 ppm to 4500 ppm with respect to the whole cathode active material. The SSZ is (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _X , (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _xz (Y ₂ O ₃ ) _z or (ZrO ₂ ) _{1-2x −z} (Sc ₂ O ₃ ) _x (CeO ₂ ) _z (0.01 ≦ x ≦ 0.2) (0.01 ≦ z ≦ 0.1), and the CSZ has a CaO content in the total weight of the CSZ. The cathode active material according to claim 11, wherein the cathode active material is 2 wt% to 17 wt%.   The positive electrode active material according to claim 13, wherein x is 0.03 to 0.20.   The positive electrode active material according to claim 2, wherein the coating layer further includes an oxide containing one or more elements of Ca, Nb, W, Mg, Ti, B, Mo, Sc and Zr. material. The chemical formula (1), wherein M ′ includes any one selected from the group consisting of Y, Zr, Ca, Sc and Ni, or a mixed element of two or more thereof. the positive electrode active material as described in 1. 2. The positive electrode active material according to claim 1 , wherein the s and v have a concentration gradient that decreases from the surface of the lithium transition metal oxide particle toward the inside.   2. The positive electrode active material according to claim 1, wherein an average particle diameter of the positive electrode active material is 3 μm to 30 μm.   The positive electrode active material according to claim 1, wherein the positive electrode active material has a compressive strength of 80 to 500 MPa under a pressure of 0.5 to 10 mN. Mixing and heat treating lithium transition metal oxide particles and composite particles;
The composite particles, see containing YSZ, GDC, LSGM, LSM, CSZ, any one or a mixture of two or more of these selected from the group consisting of SSZ and Ni-YSZ,
The method for producing a positive electrode active material, wherein the lithium transition metal oxide particles include a compound represented by the following chemical formula (1) :
Li _{(1 + a)} Ni _(1-bc) Mn _(b) Co _(c) M ′ _(s) M ″ _(v) O ₂ (1)
In the chemical formula (1), M ′ is any one selected from the group consisting of Y, Zr, La, Sr, Ga, Mg, Mn, Ca, Sc and Ni, or a mixed element of two or more of these. Including
M ″ is one or more elements of Ca, Nb, W, Mg, Ti, B, Mo, Sc and Zr;
0 ≦ a <0.2, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ s ≦ 0.2, and 0 ≦ v ≦ 0.2 . The method for producing a positive electrode active material according to claim 22 , wherein the composite particles include any one selected from the group consisting of YSZ, CSZ, and SSZ, or two or more of them. The YSZ _{is, Zr (1-x) Y} x wherein the _O is _{2-x / 2 (0.01 ≦} x ≦ 0.30), the manufacturing method of the positive active material of claim 23. The SSZ is (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _X , (ZrO ₂ ) _1-2x (Sc ₂ O ₃ ) _xz (Y ₂ O ₃ ) _z or (ZrO ₂ ) _{1-2x −z} (Sc ₂ O ₃ ) _x (CeO ₂ ) _z (0.01 ≦ x ≦ 0.2) (0.01 ≦ z ≦ 0.1), and the CSZ has a CaO content in the total weight of the CSZ. 24. The method for producing a positive electrode active material according to claim 23 , wherein the content is 2% by weight to 17% by weight. The method for producing a positive electrode active material according to claim 22 , wherein the heat treatment is performed in a temperature range of 100 ° C to 1200 ° C. 27. The method for producing a positive electrode active material according to claim 26 , wherein the heat treatment is performed in a temperature range of 100 ° C. to 600 ° C. A coating layer is formed on the surface of the lithium transition metal oxide particles by the heat treatment, and the coating layer is any one selected from the group consisting of YSZ, GDC, LSGM, LSM, CSZ, SSZ, and Ni-YSZ. Or a mixture of two or more of these,
28. The method for producing a positive electrode active material according to claim 27 , wherein the positive electrode active material includes composite particles having a single phase peak at the time of X-ray diffraction (XRD) analysis measurement. 27. The method for producing a positive electrode active material according to claim 26 , wherein the heat treatment is performed in a temperature range of 600.degree. C. to 1200.degree. Containing the composite particles inside the lithium transition metal oxide particles by the heat treatment,
The composite particles include any one selected from the group consisting of YSZ, GDC, LSGM, LSM, CSZ, SSZ and Ni-YSZ, or a mixture of two or more thereof. 29. A method for producing a positive electrode active material according to 29 . S and v in Formula (1) is characterized by having a concentration gradient that decreases toward the inside from the surface of the lithium transition metal oxide particles, producing how the positive active material of claim 22 . The composite average particle diameter _{D 50} of the particles, characterized in that it is a 500nm from 5 nm, a manufacturing method of the positive active material of claim 22. The method for producing a positive electrode active material according to claim 22 , wherein the composite particles are used in an amount of 50 ppm to 30000 ppm. The method for producing a positive electrode active material according to claim 22 , wherein the mixing is dry mixing or wet mixing.   A positive electrode comprising the positive electrode active material according to claim 1. A lithium secondary battery comprising the positive electrode according to claim 35 .

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